1. Field of the Invention
The present invention relates to an electrocardiograph which promotes easy measurement of an electrocardiogram (ECG or, more commonly EKG) over a long period of time while being carried by a subject.
2. Description of the Prior Art
In the modern medical services field, a clinical examination for measuring an ECG and a blood pressure, for example, is a common practice. Usually, this kind of examination is conducted within quite a limited period of time in a medical care institution such as a clinic or a hospital under the control of a medical doctor or an examiner or inspector of the clinical check. However, there are diseases which cannot be detected by the examination effected in a short period of time as stated above. Temporary disorder of the heart or arrhythmia, for example, often escapes the operator's attention during the examination because an unusual wave does not always clearly appear in an ECG. In many cases, therefore, it is difficult to give a determinant diagnosis through such a short time of examination.
In order to detect arrhythmia or similar disease of the kind described, there has been proposed a method for measuring an ECG over a long period of time. This method is implemented by a long-term ECG or so-called Holter ECG. Specifically, a portable electrocardiograph is put on the body of a subject of examination throughout the day or 24 hours in the daily life so as to collect and record electrocardiographic waveforms on a magnetic tape. Afterwards, while the waveforms are reproduced by a magnetic playback apparatus, an inspector such as a medical doctor observes it to find abnormality out of the waveforms and thereby conducts a diagnosis of disease such as a fugitive affection of the heart.
The electrocardiographic waveforms recorded on a magnetic tape as stated above are great in amount and, therefore, reproduced at a high speed. A problem with this prior art implementation is, therefore, that the inspector has to give a diagnosis by reading such a great amount of waveforms which are being reproduced at a high speed. Reproducing all the electrocardiographic waveforms collected over 24 hours and analyzing them by consuming a long period of time involves much wasteful work when it comes to arrhythmia which is transitory and rarely appears, resulting in low inspection efficiency as a whole.
To solve the above problem, there has also been proposed a system wherein while a magnetic tape recorded with a great amount of waveforms is reproduced at a high speed (60 times or 120 times the ordinary playback speed), an apparatus analyzes the waveforms automatically by a predetermined procedure and displays only particular portions thereof which is determined to be unusual. With this implementation, an inspector has only to examine the abnormal portions of the waveforms. However, since the electrocardiographic waveform data sequentially read out of the magnetic tape are fed to an exclusive microcomputer for analysis at a high speed due to the high-speed playback, a sufficiently long period of time cannot be allocated to the microcomputer analysis. Hence, the accuracy of analysis achievable with this scheme is limited.
A method elaborated to enhance accurate analysis has been reported recently. This method collects an ECG over a long period of time and, at the same time or on a real time basis, analyzes electrocardiographic waveforms automatically. Only the waveforms which were determined to be unusual are recorded on a magnetic tape, IC memory, or similar storage. Afterwards, only the unusual waveforms and the result of analysis are reproduced on a display which is located at the doctor's side. The doctor may print out such data for confirmation, if necessary. With this kind of approach, it is possible to allocate a 60 times or a 120 times longer period of time to the analysis than with the previously stated approach.
With the long-term and real-time analysis scheme, it is not that all the electrocardiographic waveforms collected over 24 hours are recorded but that only the waveforms determined to be unusual by the automatic analysis are recorded, as discussed above. Stated another way, the waveforms determined to be normal by the automatic analysis are simply discarded. This brings about a problem that abnormal waveforms which may have occurred in the discarded waveforms escape the doctor's attention. A prerequisite with the real-time analysis is, therefore, that abnormal waveforms be prevented from being overlooked. Also, preventing normal waveforms from being determined unusual is an important consideration in the aspect of the time and labor which would be consumed for the inspection. However, since electrocardiograhic waveforms suffer from the difference between individuals, determining whether or not they are normal by using a fixed criterion tends to increase the error rate.
As discussed above, the prior art Holter electrocardiograph needs much time and labor for examination. The apparatus is too large and heavy for a subject to carry it all through the day while dealing with routine work, imposing heavy loads on the subject both physically and mentally. Moreover, such an apparatus is expensive. While the real-time analysis type Holter electrocardiograph is successful in eliminating the problem concerning the examination or analysis time, it is not satisfactory in the aspect of reliability or accuracy of analysis and is as large and heavy as the conventional Holter electrocardiograph, again effecting the subject physically and mentally.
Recently, apparatuses capable of detecting a transitory cardiac disease by a simple procedure while reducing the loads of the subject have been reported. One of them is constructed such that when the subject feels palpitation, short of breath, vertigo or similar symptom, the subject puts the apparatus on the chest to record an ECG. Afterwards, the apparatus with the ECG is brought to a doctor and connected to an electrocardiograph to output electrocardiographic waveforms. Although this kind of apparatus is easier to carry than the conventional apparatuses, relying on the symptoms of which the subject will be conscious is problematic because an arrhythmia is not always accompanied by a subject symptom. Another problem is that the apparatus cannot always seize the decisive moment due to the interval between the time when the subject feels the symptom and the time when the subject actually puts the apparatus on the chest (the apparatus has to be pressed against the skin). Moreover, the recording time available with such an apparatus is extremely short (not longer than 1 minute) so that one may feel it awkward to go and see a doctor for the analysis of such a short ECG.
A heartbeat gauge is a further simpler apparatus recently developed in various forms. For example, the heartbeat gauge is provided with a writstwatch type configuration and has a photosensor thereinside. When the subject presses any one of the fingers against the gauge, the gauge displays a pulse frequency which the photosensor senses. Another heartbeat gauge is implemented as a wristwatch type body and a sack which has a photosensor therein and is interconnected to the body by a cable. The sack is put on the tip of a subject's finger for sensing pulses, while the body displays the pulse frequency. Still another heartbeat gauge is made up of a belt in which electrocardiographic electrodes are built in, and a wristwatch-like body. The belt is put on the subject's chest to sense the heartbeats and transmits the heart rate to the body by radio, while the body displays the heart rate. All of such gauges, however, simply display the pulse frequency or the heart rate and do not contribute to the detection of a cardiac disorder.